The neuropathology of Alzheimer's Disease (AD) is characterized by two hallmark lesions: diffuse and neuritic plaques, which are predominantly composed of the amyloid-β (Aβ) peptide, and neurofibrillary tangles, which are composed of filamentous aggregates of hyperphosphorylated tau protein (Selkoe, D. J. (2001) Alzheimer's disease: genes, proteins, and therapy, Phlysiol. Rev. 81, 741-66). Loss of neuronal synaptic density and synapse number represent another invariant feature of the disease that appears to precede overt neuronal degeneration (DeKosky, S. T. & Scheff, S. W. (1990) Synapse loss in frontal cortex biopsies in Alzheimer's disease: correlation with cognitive severity. Ann. Neurol. 27,457-64; Scheff, S. W., Scott, S. A. & DeKosky, S. T. (1991) Quantitation of synaptic density in the septal nuclei of young and aged Fischer 344 rats. Neurobiol. Aging 12, 3-12).
Notably, the memory and cognitive decline observed in AD patients correlates better with the synaptic pathology than either plaques or tangles (Terry, R. D. et al. (1991) Physical basis of cognitive alterations in Alzheimer's disease: synapse loss is the major correlate of cognitive impairment, Ann. Neurol. 30, 572-80; Dickson, D. W. et al. (1995) Correlations of synaptic and pathological markers with cognition of the elderly, Neurobiol. Aging 16, 285-98; Sze, C. I. et al. (1997) Loss of the presynaptic vesicle protein synaptophysin in hippocampus correlates with cognitive decline in Alzheimer disease, J. Neuropathol. Exp. Neurol. 56, 933-44; Masliah, E. et al. (2001) Altered expression of synaptic proteins occurs early during progression of Alzheimer's disease, Neurology 56, 127-9), and is likely the most significant factor contributing to the initial stages of memory loss (Selkoe, D. J. (2002) Alzheimer's disease is a synaptic failure, Science 298, 789-91).
Gene-targeted and transgenic mice have proven to be invaluable for addressing some of the mechanisms underlying the synaptic dysfunction (Larson, J., et al. (1999) Alterations in synaptic transmission and long-term potentiation in hippocampal slices from young and aged PDAPP mice, Brain Res. 840, 23-35; Hsia, A. Y. et al. (1999) Plaque-independent disruption of neural circuits in Alzheimer's disease mouse models, Proc. Natl. Acad. Sci. U.S.A. 96, 3228-33; Chapman, P. F. et al. (1999) Impaired synaptic plasticity and learning in aged amyloid precursor protein transgenic mice, Nat. Neurosci. 2, 271-6; Fitzjohn, S. M. et al. (2001) Age-related impairment of synaptic transmission but normal long-term potentiation in transgenic mice that overexpress the human APP695SWE mutant form of amyloid precursor protein, J. Neurosci. 21, 4691-8), although none of these models recapitulate both hallmark pathological lesions (Wong, P. C., et al. (2002) Genetically engineered mouse models of neurodegenerative diseases, Nat. Neurosci. 5, 633-9). What is needed, therefore, is an animal model transgenic for multiple Alzheimer-related genes that produces multiple major features associated with this disease, including both hallmark pathological lesions.
In generating a transgenic animal such as a transgenic mouse, a human transgene is typically microinjected into fertilized eggs from a normal, nontransgenic mouse. Such transgenic mice have, in turn, been used to generate “double” transgenic mice by mating different strains of transgenic mice, each containing a different transgene, to produce a line containing both transgenes (i.e., a double transgenic mouse line)(See, e.g., U.S. Pat. No. 5,898,094). Similarly, a double transgenic mouse can be bred with a transgenic mouse containing a third transgene to generate a triple transgenic mouse.
The disadvantages of this process of breeding triple transgenic mice are several. First, it is exceedingly time consuming to produce a multiple transgenic mouse by a series of microinjection/breeding/screening/selection steps as described above. Second, this process is very costly as it requires extensive breeding, housing, screening, and personnel costs. Third, this process produces mice with a variable genetic background, which can be a major problem for therapeutic and behavioral investigations.
What is also needed, therefore, is a process for producing multiple transgenic mice that avoids one or more of the above-listed disadvantages.